Copper Platoon Plastic Mechanics Analysis Of Continuous Extrusion

Copper bus bar is a kind of product for high current conduction. It is used not only in high and low voltage electrical appliances and electrical distribution equipment, and also in large current electrolysis and smelting works, such as fields of metal smelting, electrochemical plating and chemical caustic soda. Presently, the main technologies of producing copper bus bar are the rolling method and the common extrusion method. These two processes have several disadvantages, such as long and complex production process, high energy consumption, low material utilization and difficulty of quality controlling. Continuous extrusion forming is an ideal technology for producing copper bus bar, which has advantages in less equipment investment and high production efficiency.Continuous extrusion of copper bus bar with a high width-to-thickness ratio and expansion ratio brings forward a higher demand for extrusion mould design and extrusion machines, and it’s the fundamental of large-scale panel continuous extrusion. In view of the theoretical analysis of copper bus bar continuous extrusion mostly focus on the finite element analysis, while there is little literature about the plastic mechanical analysis of copper bus bar continuous extrusion. Therefore, the plastic mechanics analysis is employed in this thesis for theoretical research of copper bus bar continuous extrusion.By analyzing the flow pattern characteristic of metal copper in continuous extrusion, summarizing and inducing rules of the metal deformation and employing the slab method in this thesis, the pressure of continuous extrusion of copper bus bar have been calculated and analytical expression of the extrusion pressure of the inlet of expansion cavity changing with the specification of copper bus bar and parameters of extrusion mould has been obtained. At the same time, the basic UBET formula of metal plane deformation has been inducted. By employing the UBET, the upper solution of extrusion pressure of the inlet of expansion cavity and its variation with the width-to-thickness ratio, expansion ratio and parameters of extrusion mould have been obtained. Furthermore, the metal flow patterns of certain exit velocity in the expansion cavity have been studied by using UBET. By referencing the deformation rules of metal in the groove of extrusion wheel proposed in the literature, and taking the power consumed by abutment and flash in clearance into account, analytical expression of extrusion power varying with the specification of copper bus bar has been obtained. Both of the calculation results of slab method and UBET show that the extrusion pressure increases with the increment of expansion ratio and width-to-thickness ratio, and reducing the length of bearing land or enlarging the hindrance angle of extrusion mould is in favor of decreasing of extrusion pressure of the inlet of expansion cavity. The UBET result of metal flow in the expansion cavity shows that the lateral flow ability of metal in expansion cavity abates with the increasing of friction factor between the metal and expansion cavity. In addition, the calculation results of extrusion pressure of copper bus bar continuous extrusion obtained by employing slab method and UBET are compared with the experimental data. Both errors of the two methods are less than15%, and can be able to meet with the needs of practical application. Moreover, based on the calculation results, some problems emerging in the process of continuous extrusion copper bus bar with a high width-to-thickness ratio and expansion ratio such as the fracture of abutment and local plastic deformation of expansion cavity have been analyzed.The mathematical expression solution and the upper bound solution of the inlet of expansion cavity for copper bus bar continuous extrusion are obtained by plastic mechanics analysis, and they are not only expected for theoretical support of extrusion mould design and continuous extrusion machine selection, but also can provide references for the large-scale panel continuous extrusion. The formula of shear power along elements and friction power between elements and mold under different circumvents, derived in this thesis, could also provide a reference for solving other plane strain problems by employing UBET.